222 PSEUD0B0NELLIA, A NEW ECHIUROID GENUS 



containing an outer clearer portion which is sometimes slightly 

 and sometimes very highly vacuolated. 



Anterior nephridia (uteri). There is a pair of uteri which, in 

 the mature state, when laden with ova, are very prominent, pro- 

 jecting upwards and backwards from the anterior end of the 

 ventral body wall (Plate ix., figs.2, 4). They are about 6 mm. in 

 length, cylindrical in the middle, but tapering to a blunt point 

 at the extremities. Each communicates with the coelome by a 

 nephrostome, borne at the end of a relatively thick tube which 

 opens into the uterus ventrally, close to the posterior end (Plate 

 x., fig. 12). The rim of each nephrostome is prominent and is 

 distinctly crenate. The proximal end of the tube projects slightly 

 into the uterine cavity (Plate x., fig.9). Perhaps this arrange- 

 ment serves as a means for preventing the return of eggs to the 

 coeloine. In Plate x., fig.9, one may see this proximal invagin- 

 ated portion in section lying within the uterine cavity. 



Uteri from which eggs are absent are cylindrical; and in cross- 

 section the lumen can be seen to be occupied by a meshwork of 

 connective tissue trabecule which almost obliterate it in places. 

 It is in this connective tissue that the eggs come to lie imbedded 

 singly (Plate x., fig.9). Each uterus consists of an outer mass 

 of tough connective tissue containing longitudinal muscle fibres. 

 Internal to this is a highly developed, readily staining, glandular 

 layer. The external uterine openings are close to one another on 

 the ventral body wall, about 3 mm. behind the mouth. 



Male tube (andrcecium). — As in lionellia and Hamingia, the 

 male is very degenerate. It is not, however, lodged in the 

 cesophagus, uterus, or body cavity, as in these genera, but lives 

 within a definite blindly-ending tube projecting into the coelome, 

 and opening on the ventral body wall between the two uterine 

 apertures by a narrow muscular canal whose walls contain strong 

 sphincter fibres. This remarkable structure we propose to call 

 the male tube or andrcecium. Internally it is lined by a cubical 

 epithelium, continuous through the aperture with the columnar 

 epithelium of the body wall. The walls of the organ consist 

 chiefly of the invaginated dermis and epidermis, but there is also 

 a slight development of an inner circular and an outer longi- 



